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2-10
February 5, 2004
FFDM-S Service Manual
Layer Structure
The structural foundation of the DirectRay Detector is a rigid sheet of glass onto
which is formed a detector element matrix using standard thin-film Active-Matrix
Liquid Crystal Display (AMLCD) manufacturing techniques. As illustrated in
Figure 2-6, each detector element consists of a single-storage capacitor,
charge-collection electrode and an amorphous silicon (TFT) field-effect transistor
(FET) switch. The gate of each FET is connected to one of a set of gate lines and the
source of each FET is tied to one of a set of data lines.
Figure 2-6.
Perspective View of DirectRay Detector Multi-Layer Structure
The storage capacitor and charge-collection electrode are configured in such a way
that the electrode forms a “mushroom head” over much of the detector element
area. This unique design is illustrated in Figure 2-7 on page 2-11. The “mushroom”
electrode:
•
Shields the FET from the high electric field that is generated by the high
voltage applied to the top electrode
•
Shields the FET from signal charges that would collect on the insulation above
the FET
•
Increases the charge collection efficiency of each detector element by
maximizing its area
In the configuration shown in Figure 2-7, the mushroom electrode covers 86% of
the total detector element area. The mushroom electrode material blocks the
electrons from injecting into the X-ray absorber above.